Laminated closure for food trays and trays closed with same



1 E. STEPHENSON 3,298,505

LAMINATED CLOSURE FOR FOOD TRAYS AND TRAYS CLOSED WITH SAME File d Feb.12, 1965 2 Sheets-Sheet 1 E. Sfi'EPHENsoN Y 3,298,505

Jan. 17,1967

LAMINATED CLOSURE FOR FOOD TRAYS AND TRAYS CLOSED W-ITH SAME.

2 Sheets-Sheet 2 Filed Feb. 12, 1965 III," n I, n 1, I I, ,1 I, I I, I,I, I, I, I I I, I, I 1-. 2:2 3

" JAY/97,50]

ZZZ/ZZ/QTQ/ 252 6 pf? 8262972 United States Patent This inventionrelates to containers and is more particularly concerned with foodcontainers and with an improved closure for such containers.

Containers are used for many purposes, including packaging and servingprepared foods, and particularly prepared foods which may be stored incold or frozen condition and subsequently warmed in preparation forcating. Such containers generally comprise a container body, as forexample a tray of a suitable material such as aluminum or other metalfoil, and a closure for the top of the tray. In some applications it ishighly desirable that, at a particular time or during a particularperiod, the contents within the container be made available to visualobservation without completely opening the container. This enablescontainers having a variety of foods to be placed on a counter fromwhich an individual consumer may then select the desired food or type offood based on his own visual observation. Although such visualobservation is highly desirable, it is also desirable that the food beprotected against the introduction of foreign matter or bacteria whenthe heated containers are placed on display. It has consequently beenthe previous practice to provide a transparent closure for the tray toachieve these desired ends. However, transparent films commonly used forthis purpose do not by themselves provide adequate physical protectionfor the food during storage, transport, and subsequent heating.

It is accordingly an object of the invention to provide a closure forcontainers, and particularly food containers, which has excellentmechanical strength. It is a further object to provide a closure whichcan withstand the temperatures normally used for warming foods packagedin containers utilizing the closures of the invention. It is anadditional object to provide such a closure having a window which may beprotected until after the container and its contents have been heated,which window may then be exposedand left in place until serving, and theclosure then readily removed to gain access to the container contents.The accomplishment of the foregoing and additional objects will becomemore fully apparent hereinafter.

According to the invention, a closure is provided for a container, theclosure being formed as a laminated member comprising an opaquesheet-form ply of a material such as paper-board, a ply of a tnansparentfilm such as one formed of a synthetic resin, and a thermoplasticadhesive having a melting point substantially lower than that of saidfilm affixing the film to the paperboard ply. The adhesive is alsochosen so that its melting point is below or within the range oftemperature commonly required for heating or reheating of packagedfoods. when the container is heated, the heavier Paperboard layer isdelaminated from the transparent film and may be removed within an areadefined by a 'line of weakness, exposing a transparent film window. Theclosure may then in turn be subsequently readily removed to gain accessto the container contents.

The invention in its preferred embodiment is illustrated by theaccompanying drawings in which:

FIG. 1 is a top plan view of a closure member according to theinvention.

As a result,

FIG. 2 is a cross-section of the closure member.

FIG. 3 is a perspective view of a covered and sealed food container.

FIG. 4 is a cross-section of the sealed container.

FIG. 5 is a cross-section of the sealed container with the outer plyremoved from the closure, and

FIG. 6 is a cross-section of the container with the entire closuremember bearing the transparent film window removed.

Reference is now made to the accompanying drawings for a betterunderstanding of the invention, wherein all of the parts are numberedand wherein the same numbers are used to refer to corresponding partsthroughout.

Referring to FIG. 1, a closure designed according to the invention isshown comprising an opaque sheet-form member or ply 1 formed from amaterial such as paperboard. The sheet-form member 1 is provided with aperipheral line of weakness such as a score line 2 dividing the memberinto a peripheral frame 3 and a central panel 4. A tab 5 is provided atone corner connected to the central panel 4. Score lines 6 are providedto facilitate lifting the corner of the central panel 4, and tearing .ofthe panel away from the frame 3. A tab 7 is provided at one corner ofthe sheet-form member 1 to facilitate its removal from the containerflange. The border of the sheet-form member 1 is provided with diagonalslits 8, preferably diverging outwardly in the direction of pull, tofacilitate its being pulled out from the crimped over flange of thecontainer while grasping the tab 7. Scores 9 are also provided for thispurpose.

As shown in FIG. 2, a transparent film 10 is provided on the reverseside of the closure adhesively secured to the paperboard layer 1 bymeans of a thermoplastic adhesive. As employed herein, the termthermoplastic is used in its broad sense, that is, denoting a materialhaving the property of softening or fusing when heated, and hardeningand becoming rigid again when cool. The term is not used in its specialsense as sometimes applied to synthetic resins where it denotespermanently fusible materials, that is, materials which can be remeltedand cooled time after time without undergoing any appreciable change, asdistinguished from therm-oset-ting or heat-reactable resins whichundergo change upon heating. Whether the sealing material undergoeschange or not during the heating and delaminating period is immaterial.So-called heatreactable or th-ermosetting materials may be used if theadhesive can be melted and the paperboard layer delaminated and removedbefore the adhesive sets.

Any of a large number of thermoplastic adhesives may be used to laminatethe transparent film to the sheet-form member, subject to severalimportant requirements. First, the melting point of the adhesive must besubstantially lower than that of the transparent film, so that theadhesive can be heated to a temperature at or above its melting point todelaminate the sheet-form layer from the transparent film withoutmelting or in any way destroying the film. Another importantconsideration is that the melting point of the adhesive must be withinthe range of temperatures commonly used to heat foods of the type forwhich the container of the present invention is designed. Among theadhesives which may be used are waxes such as parafiin andmicrocrystalline waxes. Synthetic resins may also be used if they meetthe stated requirements, among them being ethyl cellulose hot melts,vinyl resins, either plasticized or unplasticized, butyl-or otherrubber-containing compositions, polyethylene-modified wax compositions,and the like.

Table 1 below lists a number of representative thermoplastic adhesivestogether w-ith their melting points:

3 TABLE 1 Melting Point Thermoplastic Adhesives Range- F. P-araifin wax125-185 Paraffin wax mixtures with microcrystalline wax and butyl rubberelastomer 135-195 Microcrystalline wax 135195 Wax mixtures with additionof plasticizers,

polymers, resins, metallic soaps and dyes 125-195 Low molecular weightpolymers 150-400 Thermo plastic lacquers 120350 Thermo plastic resins120-350 Thermo plastic natural gums 110-300 The adhesive shouldpreferably be substantially colorless in order to avoid interferencewith visual observation if a portion of the adhesive should remain onthe transparent film when the sheet-form member is removed.

In FIGS. 3 and 4 a covered and sealed container is illustrated,comprising a tray 11 having a flange 12 at its periphery. A crimped-overmargin 13 of the flange 12 engages the periphery of the closure andprovides a durable seal.

,The container shown in FIGS. 3 and 4, when filled with the desiredcontents and sealed, is stored in the condition shown. When the contentsare to be warmed, the entire unit is placed in such suitable warmingmeans as an oven and heated to the desired temperature. The heat causesthe paperboard layer 1 to be delaminated from the plastic film layer 10.Consequently, when the heated container is removed from the oven, thecentral paperboard panel 4 may be removed by grasping the tab andtearing the panel along the peripheral score line 2. The transparentfilm layer remains intact and permits placement of the container on ashelf, counter, steam table or the like, for viewing of the contents ofthe container and selection of a container having the desired contentsfrom a group of similar containers displaying various types of foods,while at the same time protecting the contents from contamination, asshown in FIG. 5. When the contents are to be removed from the container,the tab 7 is grasped and the sheet-form member 1 bearing the transparentfilm 10 is readily removed from the peripheral crimped over flange, asshown in FIG. 6.

The container utilized with the closure of the invention is preferablybut not necessarily in the form of a flanged tray having means providedfor engaging and securing the closure. Any tray or similar containerhaving such suitable engaging and securing means may be employed. It maybe fabricated of any one of a variety of materials such as metal foil,paper-board, plastic, etc. Aluminum foil is one preferred material,plastic another.

The sheet-form member 1 of the closure may be fabricated of any suitablematerial having the necessary mechanical strength and rigidity towithstand the rigors of shipping and storing, and offering the requiredprotection for the transparent film. Among suitable materials arepaperboard, metal foil, plastic, etc. Paperboard is the preferredmaterial.

The transparent film may be prepared from any of a number of suitablematerials such as natural and synthetic resins, and cellulosic materialsother than resins. The prime requisite of the material, in addition totransparency, and suitable mechanical properties, is that it must beable to withstand the temperatures commonly utilized in ovens withoutfusion or destruction in any other manner. Where the containers are tobe heated in common ovens, the film should be able to withstandtemperatures of at least about 180 F. When the products are designed forwarming in ovens operated at considerably lower temperatures, as forexample electronic type ovens, materials may be used for the film whichhave somewhat lower melting points. The suitable materials forfabricating the transparent film may for convenience be divided intothree classes, thermoplastic materials (those having a melting point),non-thermoplastic materials (those which do not have a melting point),and sheet materials which have no melting point and which are notinherently transparent, but which become transparent after they havesoaked up the laminating adhesive. Among the suitable thermoplasticmaterials are Saran (polyvinylidene chloride), Mylar (polyethyleneterephthalate), cellulose acetate, polypropylene, polyethylene, andethyl cellulose. Among the non-thermoplastic film are those preparedfrom regenerated cellulose, glassine papers, amylose, and parchmentizedpapers. Among the materials which become transparent as a result ofabsorption of the laminated adhesive are unfilled kraft and sulphitepapers. Mylar is the preferred material.

The composition of the film must be so chosen that it can withstand thetemperatures used in warming the food and melting the thermoplasticadhesive by which it is adhered to its protective outer sheet-form coverlayer. Moreover, when the closure is used for foods having a highmoisture content, it is desirable that a material be chosen which is notwater-sensitive.

Although a container body in the form of a relatively flat tray has beenillustrated and described and is in fact preferred, it is to beunderstood that containers of various types, shapes and sizes may beutilized with the closure member of the invention.

The closure member is formed by laminating the plastic film such asMylar to the sheet-form layer by means of the thermoplastic adhesive inconventional manner. The adhesive, as for example microcrystalline waxor a microcrystalline wax composition, may be applied first to one ofthe plies, as for example the paperboard, by any suitable means such ascoating, rolling, or spraying. The other ply, as for example thetransparent film, may then be laminated to the first ply by suitablemeans such as hot rolling.

The closure of the invention, as Well as the combination of the closureand a complementary container, have a number of advantages over closuresand containers commonly used in the art for food products. Thepaperboard cover provides protection against penetration and tearing ofthe transparent film by various objects during transportation, storageand heating, difficulties ordinarily encountered when a plastic film isused alone as a transparent closure for food containers. Moreover, theadvantages of a transparent window to enable the contents of a sealedpackage to be observed are still retained, since the paperboard layercan be readily removed when the package has been heated. Moreover, theentire closure may be readily removed by grasping the tab providedtherefor. Inasmuch as the structure of the closure lends itselfextremely well to fabrication by mass production facilities, it may beproduced at a relatively low cost. The completed package with containedfood or the like is attractive and provides an excellent seal for thecontents.

It is to be understood that the invention is not limited to the exactdetails of construction, operation, or exact materials or embodimentsshown and described, as obvious modifications and equivalents will beapparent to one skilled in the art, and the invention is therefore to belimited only by the scope of the appended claims.

I claim:

1. A laminated closure member adapted to close a container comprising asheet-form member having a first tab extending beyond the peripherythereof, a transparent film, and a thermoplastic adhesive having amelting point substantially lower than that of said film securing saidfilm to said sheet-form member, said sheet-form member having a line ofweakness defining a removable panel having a second tab extending beyondthe periphery thereof, whereby when said closure member is heated to atemperature sufiicient to melt said adhesive, said second tabmay begrasped and said panel removed to expose a window provided by said filmand whereby said first tab may be grasped for removal of said closureinember from the container which it is adapted to close.

2. A laminated closure member according to claim 1 wherein saidsheet-form member is comprised of paperboard.

3. A laminated closure member according to claim 1 wherein saidthermoplastic adhesive comprises wax.

4. A laminated closure member according to claim 1 wherein saidtransparent film is comprised of polyethylene terephthalate.

5. A laminated closure member according to claim 1 wherein saidsheet-form member is provided with oblique slits at the peripherythereof.

6. A laminated closure member according to claim 1 wherein said tabs arepositioned at diagonally opposed corners of said closure member.

7. A closed container with contained product comprising a containerbody, a laminated closure member having a tab extending beyond theperiphery thereof, and means securing said closure member to saidcontainer body, said closure member comprising a sheet-form membercomprising a sheet-form member, a transparent film, and a thermoplasticadhesive having a melting point substantially lower than that of saidfilm securing said film to said sheet-form member, said sheet-formmember having a line of weakness defining a removable panel providedwith a tab extending beyond the periphery thereof, whereby when saidclosure member is heated to a temperature sufficient to melt saidadhesive, said removable panel tab may be grasped and said panel removedto expose a window provided by said transparent film, and whereby, saidcontainer may be opened by grasping said closure member tab and removingsaid closure member.

8. A closed container according to claim 7 wherein said sheet-formmember is comprised of paperboard.

9. A closed container according to claim 7 wherein said thermoplasticadhesive comprises wax.

10. A closed container according to claim 7 wherein said transparentfilm is comprised of polyethylene terephthalate.

11. A closed container according to claim 7 wherein said container bodyis comprised of metal foil.

12. A closed container according to claim 8 wherein the periphery ofsaid closure member is provided with oblique slits to facilitate itsremoval from said container.

13. A closed container according to claim 8 wherein said first tab andsaid second tab are positioned at diagonally opposed corners of saidclosure member.

14. A closed container with contained product comprising a containerbody formed of metal foil, and a laminated closure member retained by acrimped-over flange of said container body, said closure member beingprovided with a tab extending beyond the periphery thereof andcomprising a sheet-formed paperboard member, a transparent film, and athermoplastic adhesive having a melting point substantially lower thanthat of said film securing said film to said sheet-form member, saidsheet form member having a line of weakness defining a removable panelprovided with a tab extending beyond the periphery thereof, whereby whensaid closure member is heated to a temperature sufficient to melt saidadhesive, said removable panel tab may be grasped and said panel removedto expose a window provided by said transparent film, and whereby saidcontainer may be opened by grasping said closure member tab and removingsaid closure member.

15. A closed container according to claim 14 wherein the periphery ofsaid closure member is provided with oblique slits to facilitate itsremoval from said container.

16. A closed container according to claim 14 wherein said first tab andsaid second tab are positioned at diagonally opposed corners of saidclosure member.

7. A CLOSED CONTAINER WITH CONTAINED PRODUCT COMPRISING A CONTAINER BODY, A LAMINATED CLOSURE MEMBER HAVING A TAB EXTENDING BEYOND THE PERIPHERY THEREOF, AND MEANS SECURING SAID CLOSURE MEMBER TO SAID CONTAINER BODY, SAID CLOSURE MEMBER COMPRISING A SHEET-FORM MEMBER COMPRISING A SHEET-FORM MEMBER, A TRANSPARENT FILM AND A THERMOPLASTIC ADHESIVE HAVING A MELTING POINT SUBSTANTIALLY LOWER THAN THAT OF SAID FILM SECURING SAID FILM TO SAID SHEET-FORM MEMBER, SAID SHEET-FORM MEMBER HAVING A LINE OF WEAKNESS DEFINING A REMOVABLE PANEL PROVIDED WITH A TAB EXTENDING BEYOND THE PERIPHERY THEREOF, WHEREBY WHEN SAID CLOSURE MEMBER IS HEATED TO A TEMPERATURE SUFFICIENT TO MELT SAID ADHESIVE, SAID REMOVABLE PANEL TAB MAY BE GRASPED AND SAID PANEL REMOVED TO EXPOSE A WINDOW PROVIDED BY SAID TRTANSPARENT FILM, AND WHEREBY, SAID CONTAINER MAY BE OPENED BY GRASPING SAID CLOSURE MEMBER TAB AND REMOVING SAID CLOSURE MEMBER. 